1. Field of the Invention
The present invention generally relates to sports racquets and, more particularly, is concerned with devices for applying variable tension to different length string sections of a sports racquet stringing bed and for holding the stringing tension to achieve more uniform stringing stiffness across the ball playing face of the racquet and thereby enhance feel and performance of the racquet.
2 Description of the Prior Art
A conventional sports racquet, such as a tennis racquet, has a frame which includes a head portion, a throat portion and a handle portion formed as an integral structure. Typically, the racquet frame is fabricated of composite-type material composed of high modulus fibers such as graphite fibers or glass fibers in a matrix of an epoxy resin. Alternatively, racquet frames have been fabricated from other materials, such as aluminum, wood and plastics.
The head portion of the racquet frame typically has a generally round, such as circle or oval, configuration and contains outer and inner pluralities of spaced stringing holes extending through outer and inner circumferentially-extending, radially-spaced walls of the round head portion. The head portion also typically mounts a plurality of cylindrical hollow grommets between the walls which are aligned with paired holes of the outer and inner pluralities of holes. A bed of stringing extends in a grid pattern across an open region encompassed by the head portion and through the holes and grommets. The stringing bed is applied under tension across the open region of the head portion to provide a ball striking face of the racquet.
Commonly, the stringing of the racquet is composed of animal gut, synthetic material, or metallic materials. Because of the round configuration of the head portion of the racquet, the bed of stringing installed in the head portion will contain string sections having different lengths. The string sections nearest the longitudinal and transverse axes of the head portion will be the longest, while those nearest the periphery of the head portion will be the shortest.
Heretofore, the normal method by which racquets have been strung is by pulling tension on the string sections at the same tension level. It is apparent that a lower stiffness will be imparted to the longer string sections than to the shorter string sections of the stringing bed, producing a non-uniform stiffness throughout the stringing bed across the longitudinal and transverse axes of the racquet. Such non-uniformity of stringing bed stiffness results in a non-uniform rebound of a ball off the stringing bed when struck at different locations thereon. The effect of such non-uniformity of stiffness is that the area of the stringing bed which has the least stiffness and thus produces the highest degree of power, control and feel is near the center of the stringing bed. However, this area is relatively small in comparison to the overall area of the stringing bed
It is therefore desirable to provide a bed of stringing of more uniform stiffness so that the rebound of the ball off the stringing bed of the racquet is more uniform across the entire area of the stringing bed to improve the feel and performance of the ball playing face of the racquet. Techniques have been proposed in the prior art to produce this desired effect. U.S. Pat. Nos. 4,330,132 and 4,408,760 to Ferrari disclose a sports racquet in which individual string sections of different lengths are pulled at different tensions.
However, the technique disclosed in the Ferrari patents for holding and maintaining the differential tensions involves the use of wedges which must be installed into the passages of the grommets of the racquet. This poses a problem if the grommet passage is too small to accept both the wedge and string. Also, pulling different lengths of string sections at different tensions poses another problem. The need to keep changing the tension setting of the stringing machine for each different length of string section can be time-consuming and tedious. Also, the technique is dependent upon whether the operator can be relied upon to not forget to change the tension settings while stringing the racquet.
Consequently, a need still exists for improvement of the techniques for tensioning the racquet stringing bed so as to overcome the problems associated with prior art techniques.